The identifying tag !HPF$ must be spelled correctly. Misspelling the tag is a common programming bug which is difficult to detect. For example, if you leave the dollar sign ($) off of the end of the tag, the entire line is treated as a comment. For example:
!HPF DISTRIBUTE a(BLOCK)
This misspelled line is interpreted as a comment, because it begins with an exclamation mark (!). This does not always affect program results, but it can cause performance degradation.
